Flash MX 2004 Games : Art to ActionScript

Chapter 13: Small games to keep them loading
The code that is contained within the ‘if ’ statement flips the ‘moveX’ variable and updates the
value for ‘ballX’ so that it is at the position of the previous frame. It is possible that the next time
this code is run the value for ‘ballX’ is still greater than 57, in which case if we had not added the
further condition that ‘moveX’ has to be greater than zero then the code within the ‘if ’ statement
would be executed again, flipping ‘moveX’ a second time, so the ball would stick to the wall. But
the test for ‘moveX’ ensures that the ball will bounce freely from the wall.
The next ‘if ’ statement tests for a collision with the top wall and behaves identically to the test
for the sides; this time we test for the value of ‘ballY’ only when the direction is up, ‘moveY’ is
less than zero. At this point we update the ball. Then we test for a collision with the ‘board’ clip.
This can only happen when the ball is moving down, ‘moveX>0’ and the y value of the ball is
19. The use of an exact value like this means that you cannot change the direction value or the
initial start position without adjusting this value. I point this out because it is a coding technique
to discourage. Because the initial y position for the ball is −23, and the increments are in threes
the ball will eventually hit the value 19.
−23 + 14 ∗ 3 = 19
But if you change anything it won’t. Yuck! It would be much better to make 19 the goal value.
If we want to make sure the test only occurs once then add in another test to make
if (moveX>0 && ballY>=19 && ballY0 && ballY>=19 && ballY